This application is based upon and claims the benefit of Japanese Patent Applications No. 2000-167823 filed on Jun. 5, 2000 and No. 2000-178785 filed on Jun. 14, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a semiconductor pressure sensor having a diaphragm that is formed by a recess formed on a semiconductor substrate for detecting a pressure.
2. Description of the Related Art
JP-A-11-97413 proposes a diaphragm type semiconductor pressure sensor in which a recess is formed on a semiconductor substrate (silicon substrate) by anisotropic etching to form a diaphragm on a bottom of the recess for receiving a pressure. Bottom side corner portions of the recess defining the diaphragm (back surface of the diaphragm) are rounded by means of isotropic etching to improve a breaking strength of the diaphragm. That is, the back surface edge portion of the diaphragm has an R-shape in cross-section. However, it is found that if the edge portion is rounded excessively, the etching time is lengthened to reduce the throughput.
The present invention has been made in view of the above problems. An object of the present invention is to provide a diaphragm type semiconductor pressure sensor in which a back surface edge portion of a diaphragm can be rounded efficiently while keeping a sufficient breaking withstand pressure of the diaphragm.
According to an aspect of the present invention, a semiconductor pressure sensor has a recess formed on a semiconductor substrate by anisotropic etching. The recess has a sidewall, a bottom wall that serves as a diaphragm for detecting a pressure, and a corner portion provided between the sidewall and the bottom wall and having a radius of curvature R. The radius of curvature R satisfies a formula of:
R/S=526xc2x7(d/S)2xe2x88x920.037xc2x7(d/S)+a1, 
where S is an area of the diaphragm, d is a thickness of the diaphragm, and a1 is in a range of 9.6xc3x9710xe2x88x927 to 16xc3x9710xe2x88x927 inclusive. In this case, the corner portion can be rounded efficiently for a short etching time by anisotropic etching.
According to another aspect of the present invention, a bonding surface of a base having a pressure introduction passage is bonded to a semiconductor substrate having a recess and a diaphragm as a bottom wall of the recess. A bonding angle defined between a sidewall of the recess and the bonding surface of the base is equal to or larger than 80xc2x0 so that a separation withstand pressure of a bonding portion where the base is bonded to the semiconductor substrate is larger than a breaking withstand pressure of the diaphragm. A length of a portion defining the bonding angle equal to or larger than 80xc2x0 holds preferably 50% at least, and more preferably 80% at least with respect to an entire length of the bonding portion surrounding the recess.